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G. W. Asher, A. J. Peterson and J. J. Bass

Summary. At monthly intervals during the year blood samples were collected every 20 min for 12 h from 4 entire and 2 prepubertally castrated adult fallow deer bucks. In the entire bucks there were seasonal changes in mean concentrations and pulse frequencies of plasma LH. Mean concentrations in late summer and autumn were 3–6 times higher than during other seasons. LH pulse frequency was low (0–1 pulses/12 h) during most of the year and increased only during the 2-month period (January and February) that marked the transition from the non-breeding season to the autumn rut. During this period there was a close temporal relationship between pulses of LH and testosterone. However, during the rutting period (March and April) episodic secretion of testosterone, manifest as surges in plasma concentrations of 4–6 h duration, was not associated with any detectable pulses in LH although mean plasma concentrations of LH remained elevated. During the rut, the surges of plasma testosterone occurred at similar times of the day. Plasma profiles in May indicated very low concentrations of LH and testosterone secretion in the immediate post-rut period. Castrated bucks exhibited highly seasonal patterns of LH secretion, with mean plasma LH concentrations and LH pulse frequency being lowest in November (early summer) and highest in February and March (late summer–early autumn). Mean concentrations and pulse frequency of LH in castrated bucks were higher than for entire bucks at all times of the year.

Keywords: fallow deer; reproduction; pituitary; testis; LH; testosterone

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J. J. Bass, A. S. McNeilly and H. E. Moreton

Summary. In bulls there was no increase in plasma FSH and only a small increase in LH over the first 14 weeks of age. In steers (castrated) plasma LH and FSH were unchanged for the first 3 weeks but increased significantly at 7 and 14 weeks. After 100 μg Gn-RH, LH release in bulls was minimal until 7 and 14 weeks and there was no comparable rise for FSH. LH and FSH responded to Gn-RH throughout the trial in the steers. The neonatal calf testes selectively inhibited the release of FSH from the pituitary even when challenged with Gn-RH.

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R. W. Moore, J. J. Bass, G. W. Winn and H-U. P. Hockey

Summary. Weaned Romney ewe lambs were grazed at two levels of nutrition from 20 December to 12 April. Both groups were grazed together at a high level of nutrition thereafter. Vasectomized rams were introduced on 1 April. Oestrus occurred in 62/84 (74%) of the low nutrition group and in all 24 of the high nutrition group. The mean date of first oestrus was 3 June for the former and 28 May for the latter. The non-oestrous ewes were killed on 17 July and the others within 5 days of showing oestrus. From each carcass, certain organs (i.e. adrenals, ovaries, thyroid, heart, kidneys, liver, lungs, spleen, stomach and uterus) and various fat depots were dissected out and weighed. In addition, half of the carcass was minced and subsampled for protein and fat analysis.

The weight of uterus discriminated between oestrous and non-oestrous animals, as did a linear combination of the weights of lungs, spleen and stomach. The data suggest that fatness or protein content, or the weights of the other organs, are not important indicators of sexual maturity in female sheep.

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S. Y. W. Chant, P. K. Chakraborty, E. J. Bass and D. E. Wildt

Summary. Treatment of pregnant cats with FSH on Days 33–37 and hCG on Days 38 and 39 induced development of vesicular follicles (mean 9·3 follicles/cat), ovulation (mean 3·4 corpora lutea/cat) and behavioural oestrus (5/7 cats). In the gonadotrophin-treated females, oestradiol-17β concentrations gradually increased but serum progesterone levels remained constant although in saline-treated females mean serum oestradiol-17β concentrations remained basal and progesterone concentrations gradually declined. The results indicated that (1) the feline ovary and related mechanisms for inducing sexual receptivity were not refractory to exogenous gonadotrophic stimulation during mid-gestation and (2) hCG administered after serial injections of FSH during pregnancy may potentiate ovarian oestradiol-17β secretion.